2 is
a block diagram of the SONET multiplexer supporting contiguous concatenated STS-3c
and STS-12c payloads.
Virtual Concatenation and LCAS Virtual concatenation allows an arbitrary number of
STS-1s to be concatenated and transported across a SONET network. The STS-1s do
Figure 10.2 SONET contiguous concatenation
3:1
4:1
3:1
4:1
OC-48
STS-3
STS-3
STS-1
STS-1
STS-1
STS-1
STS-1
STS-1
STS-3c
STS-12c
270 Chapter 10
not need to be contiguous and can be transported independently across the network
and recombined at the transmission endpoint. Only the source and destination are involved
in the virtual concatenation process. virtual concatenation allows concatenation
of up to 256 STS-1/STS-3c SPEs and up to 64 VT1.5/2/3/6 SPEs. Figure 10.3 is a block
diagram illustrating the capabilities of virtual concatenation for STS rates.
Link Capacity Adjustment Scheme (LCAS) is a two-way handshake protocol designed
to change the capacity of a virtual concatenated signal dynamically . LCAS must be
used in conjunction with virtual concatenation and is not able to create or adjust the
virtual concatenated circuit. Virtual Concatenation is used to build the pipe, and LCAS
dynamically defines which of the concatenated group members is carrying traffic.
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